Footwear in general has a sole made of rubber, leather or an synthetic or any other suitable material. The sole conducts or convects heat into the interior of the footwear. In warm climate or when it is warm in other regions the heat from the ground is transferred to the foot of a wearer through the sole. As footwear is usually shaped to enclose substantially all of the feet and is generally fairly well insulated against the environment the temperature inside the footwear quickly builds up to a level which is uncomfortable.
As human feet and hands have a relatively higher number of sweat glands per square centimeter than other parts of the body the inside of the footwear also quickly becomes damp due to sweating.
The temperature and dampness inside the footwear promote growth of algae and the footwear becomes unhygienic and usually also has an unpleasant odour. They also affect work efficiency. As much of the heat travels upward to the head and people tend not to concentrate well in this situation.
In recent years many sports such as tennis, hockey and soccer are played on synthetic surfaces, the surface temperatures of which can be as high as 60 to 70 degrees centigrade. The temperature inside the players' footwear is even higher. Long distance runners are also affected by high temperatures in footwear. Many players cannot perform to the level they are capable in this environment. Injuries through sore feet and blisters are also prominent.
An inner sole worn in footwear has been available for sometime as a source of comfort to the wearer. It is usually made of an absorbent foam material. But this inner sole does not reduces the temperature in the footwear and it does not take long for it to be saturated with sweat and thereafter the wearer continues to suffer the above discomfort.
More recently footwear with ventilation openings for cooling its interior has been introduced into the market. These openings however result in weakened zones and the strength of the footwear is greatly compromised.